1. Field of the Invention
The present invention relates to button or coin shaped secondary batteries and capacitors capable of being reflow soldered and, more particularly, to the structure of secondary battery or capacitor having terminals.
2. Description of the Related Art
Coin or button shaped primary and secondary batteries and capacitors which are used as auxiliary power supplies for backup for clocks and memories of portable devices are generally fitted with terminals for taking leads from the positive and negative electrodes of the batteries in use.
With respect to their terminal shapes, components have decreased in size in recent years. In a known type, terminals are inserted into a mounting board or substrate provided with holes for terminals, and the terminals are soldered from the rear side of the substrate (FIGS. 1 and 2). Also, the surface mount type (FIGS. 3-6) is prevalent. In particular, a secondary battery or capacitor fitted with terminals is placed on a substrate intact. Solder-plated portions at the front ends of the terminals are placed on the front surface of the substrate. A soldering operation is performed from this front side of the substrate. The terminals of the surface mount type are so shaped that both positive and negative terminals extend a considerable distance outwardly from the outer surface of a button or coin shaped secondary battery or capacitor, for the following reason. The positive and negative terminals are hand soldered to the substrate and so the secondary battery or capacitor is protected from thermal effects.
Recently, button or coin shaped secondary batteries and capacitors have been increasingly required to be capable of being reflow soldered in order to streamline mounting operations. In the past, gaskets made of polypropylene were used. Secondary batteries and capacitors which use better heatproof gaskets made of thermoplastic engineering materials such as polyphenylene sulfide and which can be reflow soldered have been devised and put into practical use.
To surface-mount a secondary battery or capacitor, which can be reflow soldered, to a substrate, it has been necessary to bring the surfaces of the positive and negative terminals into parallel contact with the substrate surface simply if the secondary battery or capacitor having the terminals is placed on the substrate surface. with respect to the terminal shape, where the positive and negative terminals are directed in the same direction (FIGS. 7 and 8), the center of gravity of the secondary battery or capacitor having the terminals has poor balance. This is unsuited for surface mounting. Where positive and negative terminals are directed in opposite directions (FIGS. 3-6; spaced apart by 180xc2x0), both positive and negative terminals easily make parallel contact with a substrate. Therefore, this type is advantageous for surface mounting and has become a mainstream.
With respect to terminal shapes of surface mount type secondary batteries and capacitors that can be reflow soldered, the shape type in which positive and negative terminals are spaced apart by 180xc2x0 and directed in opposite directions is mainstream. This shape has the disadvantage that where a secondary battery or capacitor with terminals is surface-mounted to a substrate by a reflow process, the secondary battery or capacitor with terminals occupies a large area on the substrate. As components have been required to be fabricated in smaller size, it is quite important to minimize the area occupied on the substrate by the secondary battery or capacitor with terminals.
The present invention provides a structure, where either one of positive and negative terminals is placed within a square that the outer surface of a button or coin shaped secondary battery or capacitor inscribes. This greatly reduces the area taken up on the substrate by the secondary battery or capacitor fitted with the terminals.
Where the negative electrode side is placed opposite to the substrate surface, the positive electrode can and the negative terminal are brought into contact with each other by the weight of the secondary battery or capacitor after reflow solder. This creates the possibility that the positive and negative electrodes are shorted to each other. To prevent this electrical shorting, at least one step is formed on the negative terminal mounted on the negative electrode can opposite to the substrate surface. Further details of the configuration of the present invention are as follows.
(1) A secondary battery or capacitor fitted with terminals. The positive and negative terminals are mounted to the secondary battery or capacitor to take leads. Either one of these two terminals is placed substantially within a square that the outer surface of the secondary battery or capacitor inscribes.
(2) A secondary battery or capacitor fitted with terminals. The positive and negative terminals are mounted to the secondary battery or capacitor. The solder-plated portions of the positive and negative terminals are placed parallel to the substrate surface on which the secondary battery or capacitor is mounted.
(3) A secondary battery or capacitor fitted with terminals including a terminal opposite to the substrate surface on which the secondary battery or capacitor is mounted. The terminal opposite to the substrate surface has at least one step.
Generally, many of electronic components mounted on substrates are rectangular in shape. Therefore, where a round secondary battery or capacitor is mounted, dead space is created. As shown in FIG. 15, dead space is often created at the corners of a square 5n where the outer surface of a secondary battery or capacitor inscribes the square 5n. Therefore, a terminal 5c connected with an electrode located on the side of a substrate is preferably made smaller. However, the size can be increased within the range of the square 5n. If the terminal 5c is too small, the secondary battery becomes unstable. Therefore, the width 5L is preferably set to more than 40% of the diameter R of the secondary battery. It is also necessary to set the width 5L to less than the diameter R of the secondary battery or capacitor so that the outside diameter of the battery or capacitor does not go beyond the inscribed square 5n. 
Where stability occurring when a secondary battery is placed on a substrate is taken into consideration, the end of the terminal 5c should not be too close to the center of the secondary battery or capacitor. Where the distance from the end of the terminal 5c to the outer surface of the secondary battery or capacitor is 5m and the radius of the battery or capacitor is r, it is important to have 0xe2x89xa65m less than r.
However, depending on the accuracy at which the terminal is welded, the terminal 5c may jut a distance equal to about 10% of the diameter of the secondary battery or capacitor out of the square 5n. This extent is within the scope of the present invention.
Since a terminal 5b connected with an electrode located on the opposite side of the substrate juts out of the inscribed square 5n, the size is preferably made as small as possible. The stability of the secondary battery or capacitor is secured by making the terminal 5c wide. This makes use of the dead space and allows more substantial high-density packaging. Consequently, the width 5L of the terminal 5c, at its end, connected with the electrode on the substrate side and the width 5k of the terminal 5b, at its end, connected with the electrode located on the opposite side of the substrate preferably satisfy 5k less than 5L.
The terminal 5b connected with the electrode located on the opposite side of the substrate does not need to be positioned on a line with the terminal 5c. The packaging efficiency is also effectively increased by slightly tilting the terminal 5b such that it is located in a dead space at one corner of the inscribed square 5n. In this case, it is necessary to stabilize the secondary battery or capacitor by placing the center 5g of the secondary battery or capacitor within a triangle created by the positions 5h, 5i at which the ends of the terminal 5c connected with the electrode on the substrate side are located at corners and by the midpoint 5j between the ends of the terminal 5b connected with the electrode on the opposite side of the substrate.
In this way, the shapes and positions of the terminals 5b and 5c are determined as long as they jut out of the secondary battery or capacitor slightly within a tolerable range of stability.
In the terminal shape of surface mount type terminals of a secondary battery or capacitor which can be reflow soldered, the area occupied on a substrate by the secondary battery or capacitor fitted with the terminals can be reduced greatly by placing the terminal mounted opposite to the substrate surface within a square that the outer surface of the secondary battery or capacitor inscribes provided that the terminal mounted opposite to the substrate surface juts out of the perimeter of the square that the outer surface of the battery or capacitor inscribes. With this terminal shape, the terminal cannot be hand soldered to the substrate, because either one of the positive and negative terminals does not protrude out of the perimeter of the square that the outer surface of the secondary battery or capacitor inscribes. However, the terminal shape in accordance with the present invention permits mounting to the substrate using a reflow process. That is, the secondary battery or capacitor is passed through a reflow furnace to heat the whole battery or capacitor, and solder previously applied to the substrate is used to solder the terminal portions. Where the secondary battery or capacitor is surface-mounted, space savings can be very effectively achieved.
Where the negative electrode is placed opposite to the substrate surface as shown in FIG. 14, the positive terminal can and the negative terminal may be brought into contact with each other by the weight of the secondary battery or capacitor after reflow soldering, thus creating the possibility that the positive and negative electrodes are shorted to each other. This electrical shorting can be effectively prevented by providing at least one step on the negative terminal mounted on the negative terminal can opposite to the substrate surface.
It is impossible to eliminate variations in height between individual secondary batteries or capacitors for manufacturing reasons. Therefore, where no step is formed on the terminal connected with the electrode located on the substrate side, if the height of the secondary battery or capacitor decreases, the terminal connected with the electrode on the opposite side of the substrate will float off the substrate. As a result, electrical connection with the substrate may not be made. Variations in height between individual secondary batteries or capacitors can be absorbed by an amount corresponding to the step. The step may be set, taking account of the height variations. Where a terminal having a step is used, if the height of the secondary battery or capacitor deviates from a target value, the surface of the terminal that is electrically connected with the substrate may not be parallel to the substrate. In this case, the portion (i.e., a portion bent because of the presence of a step or the end portion of the surface of the terminal that is electrically connected with the substrate) that rises from the surface of the terminal that is electrically connected with the substrate comes into contact with the substrate. During reflow, the solder begins to melt at this location and is electrically connected. It is very advantageous to place solder at this location. The method of placing solder can be dipping, plating, or other method. No limitations are imposed on this method.